For purposes of an exemplary showing, the present invention will be described in its application to moving stairways or escalators. As will be abundantly apparent to one skilled in the art, the teachings of the present invention are equally applicable to walkways of the type comprising an endless procession of tread segments or pallets moving between a pair of balustrade skirts.
As is well known in the art, the typical escalator comprises a plurality of steps which are operatively joined together in a pivotal fashion to form an endless loop of steps. Each step comprises a pair of side frames which supports a substantially planar tread and an arcuate riser. Each step has a first pair of shaft mounted wheels located to either side thereof and substantially beneath the riser. Each step has second pair of shaft mounted wheels located near the opposite end of the tread remote from the riser. The shaft of the second set of wheels is also operatively attached to a pair of chains which passes over an upper pair of sprocket wheels at the upper end of the escalator and a lower pair of sprocket wheels at the lower end of the escalator. One of the upper and lower sprocket wheel pairs is an idler pair, and the other of the upper and lower sprocket wheel pairs is a driven pair, driving the pair of chains and the plurality of steps attached thereto. The set of tracks for the first set of wheels is so configured that it assures that the treads of the steps in the passenger carrying flight are horizontal. The set of tracks for the first set of wheels is further configured to assure that the treads assume a continuous belt-like configuration about the upper and lower sprocket wheel sets and throughout the return flight. The second set of shaft mounted wheels rides upon its own separate set of tracks.
The overall framework of the escalator assembly also mounts a pair of balustrades, which support moving handrails, as is well known. At least in the area of the moving steps, the balustrades are provided with continuous skirts between which the steps pass. The skirts are made of adjacent panels of low friction material such as stainless steel or enameled metal.
As will be appreciated, because of their length it is virtually impossible to provide balustrade skirts which are perfectly planar and totally free of waiver. The steps are generally fabricated or cast of metal and by virtue of their fabrication or casting may vary slightly in dimensions within acceptable tolerances. Furthermore, to prevent binding there must be a certain amount of play between the first and second sets of wheels of each step and their respective sets of rails. Bearings provide additional play, and all of these elements contribute to some lateral or side-to-side shifting of the steps during their travel. This lateral motion may be amplified by wear and uneven loading of the tread due to the position of the passenger.
From the above, it will be understood that a small gap between the moving stairway and each of its skirts must be provided. In fact, differences in the distance between the skirts at various positions along their length, variations in the width of the steps as a result of the manner in which they are manufactured, tolerances, alignments, and the like assure that these gaps are, indeed, unavoidable. Failure to provide gaps between the stairway and the adjacent balustrade skirts would result in binding, wear, vibration and noise. By code, in the United States, the gap between each step side and the adjacent balustrade skirt is not to exceed 3/16 inch.
It is desirable to minimize the width of these gaps to prevent foreign material from getting into the escalator mechanism. More importantly, however, it is desirable to minimize these gaps for reasons of safety. The narrower these gaps are, the less chance there is that the clothing, footwear or extremities of a passenger could be drawn into either of these gaps resulting in damage to the clothing and injury to the passenger.
Prior art workers have approached this problem in a number of different ways. One approach has been to provide lateral guidance for the moving stairway to minimize lateral movement thereof. An example of this is taught in U.S. Pat. No. 2,813,613 wherein castors are mounted on the brackets of each step, and engage and ride along the skirts. British patent specification 519,149 teaches the provision of an edge rib on either end of each tread, the edge rib being so configured as to make the passenger slightly uncomfortable should he step upon it so that he will automatically move his foot inwardly from the edge of the step tread and away from the adjacent gap.
U.S. Pat. No. 3,144,118 teaches the application of low friction coatings on the skirt thereby reducing the chances of clothing, footwear or the like being drawn into the gap by the relative movement of the steps and the skirts. U.S. Pat. No. 3,191,743 teaches a moving walkway wherein the skirts are provided with resilient ribs which extend into and ride through the first tread groove at each side of each tread.
U.S. Pat. No. 2,981,397 teaches the provision of a removable resilient cleat along each side edge of each step tread. If the weight of the passenger is applied to this cleat, it will bend toward the skin, closing the gap therebetween. In a somewhat similar fashion, British patent specification 1 276 922 teaches the provision of a barrier means affixed to each side of each stair tread. The barrier means prevents the passenger's foot from approaching either gap between the tread sides and the adjacent skirts.
U.S. Pat. No. 3,986,595 teaches a safety device located at either side of each step of an escalator. If the passenger should contact the safety device, it will shift to close the gap between the step side and the adjacent skirt. U.S. Pat. No. 4,374,558 teaches an escalator step wherein the tread is provided with front-to-rear ribs which are formed on a press. The endmost portions of the tread are formed without ribs. Ribbed inserts are attached to the tread in these endmost ribless areas and are so located to assure that each tread has the same predetermined side-to-side dimension.
Finally, U.S. Pat. Nos. 4,236,623; 4,397,383; 4,413,719 and 4,519,490 teach the provision of resilient inserts mounted along the side edges of each tread so as to minimize the adjacent tread/skirt gap. In some instances, any pressure applied to the resilient strips will cause them to form a closure seal with the adjacent skirt. In some instances, the resilient members have portions which actually contact the skirt substantially continuously.
All of these approaches have both advantages and disadvantages. Where actual substantially continuous contact between a gap closing member and an adjacent skirt takes place, wear will result, and sometimes noise and vibration will result as well. None of these approaches provide an adjustable gap minimizing means, enabling a final adjustment of the assembled escalator.
The present invention is based upon the discovery that better results can be achieved by providing steps having treads with conventional fore-to-aft alternate ribs and grooves, but with a predetermined number of ribs removed at each side of the tread to provide planar surfaces at each tread side. Separate ribbed tread inserts are affixed to the planar tread surfaces and are laterally adjustable thereon. Riser inserts may also be affixed to the side edges of the riser of each step. The adjustable inserts avoid a non-conformance product assembly; enable reasonable tolerances in the manufacture of the parts of the escalator; and enable reasonable tolerance in the alignment of the escalator track system and the balustrade skirts.
The ribbed inserts are preferably made of ultra-high molecular weight plastic. Attachment and adjustment of the tread inserts constitute the final adjustment of the escalator during its assembly and installation. The gap between each tread insert and the adjacent skirt is preferably set at about 1/16 inch on a static basis.